1. Field of the Invention
The present invention relates to electrical connectors, and, in particular, to plugs designed to reduce crosstalk between adjacent transmission paths.
2. Description of the Related Art
One type of plug used to terminate cordage (i.e., multi-wire cabling) is the 110-type patch plug, manufactured by Lucent Technologies, Inc., of Murray Hill, N.J. One end of the 110-type patch plug permanently terminates a multi-wire cable, while the other end mates removably to the insulation displacement contacts (IDCs) of a 110-type connecting block, which is also manufactured by Lucent Technologies. 110-type patch plugs are often used in voice and data transmission applications. In such transmissions, a balanced signal transmission path is formed by each pair of conductors, called the TIP conductor and the RING conductor. A typical 8-wire cable can therefore support four different voice or data signal transmission paths.
A 110-type patch plug has one or more pairs of contacts (typically 1, 2, 3, or 4 pairs) that form the electrical connections between the conductors of a multi-wire cable and the IDCs of a 110-type connecting block. One end (i.e., the mating end) of each patch-plug contact is a blade that engages a split-beam contact of the 110-type connecting block. The other end (i.e., the cable end) of each patch-plug contact has a split-beam contact (e.g., an IDC) that terminates one of the cable conductors. The blades are sequenced in a linear alternating fashion between TIP and RING conductors in order to be aligned with the split-beam contacts of a 110-type connecting block.
FIGS. 1A-C shows perspective, top, and side views of the contacts of a prior art 110-type patch plug. The 110-type patch plug of FIGS. 1A-C has four pairs of contacts, with each TIP-RING pair (T.sub.i, R.sub.i) corresponding to a single balanced transmission path. Due to the proximity of the transmission paths within this 110-type patch plug, signals in one transmission path can induce near-end crosstalk in one or more adjacent transmission paths within the same plug.
Near-end crosstalk refers to unwanted signals induced in one transmission path due to signals that are transmitted over one or more other transmission paths appearing at the end nearest to where the transmitted signals are injected. Near-end crosstalk often occurs when the wires, contacts, and/or other conductors that form the various transmission paths are in close proximity to one another.
What is needed are patch plugs and other connectors that are designed to have low crosstalk between the transmission paths of multi-wire circuits. Previous attempts at reducing crosstalk have involved increasing the distance between transmission paths (i.e., from one pair of TIP-RING contacts to another) and/or decreasing the distance within each transmission path (i.e., between the two contacts of a single TIP-RING pair). Another approach is to introduce opposing crosstalk that is out of phase with the existing crosstalk. This is often done by designing a cross-over (i.e., a physical crossing of one contact over another) in one or more TIP-RING pairs, while possibly leaving other pairs of contacts without a cross-over. The patch plug of FIGS. 1A-C introduces opposing crosstalk by utilizing inductive coupling. These techniques work to some degree for low-frequency transmissions (e.g., less than 1 MHz), but do not provide satisfactory levels of crosstalk reduction for transmissions having relatively high frequencies.